Submersible vehicles require propulsion systems that are efficient and reliable in deep-sea environments. In addition, counterrotating shafts are desirable in some applications. Typically, propeller drive motors are used which provide 20HP at less than 500 rpm. Present day submersibles such as torpedoes and autonomous underwater vehicles (hereinafter also referred to generically as autonomous underwater vehicles) characteristically employ either DC motors, having slip rings and brushes, wherein both the stator and rotor are rotated, or permanent magnet brushless DC motors which do not have counterrotating shafts. Moreover, both motors typically require the use of a gear box. It will be appreciated that conventional DC motors that employ slip rings and/or brushes, suffer a number of disadvantages and problems, including dirt and dust buildup associated with the slip rings, brushes, gearbox speed reducers and the like. Further, the arcing associated with such slip rings and brushes can create a serious hazard in underwater vehicles.
Patents of possible interest in the field of motors include U.S. Pat. Nos. 4,169,983 (Felder); 4,358,693 (Palmer et al); 4,371,801 (Richter); and 4,503,349 (Miller). Briefly considering these references, the Palmer et al patent discloses a permanent magnet motor wherein rotors and stators are alternately disposed along a common shaft on which the rotors are mounted. The Miller patent discloses a pulse generator including a pair of rotors positioned within a stator and mounted for rotation in opposite directions. The Richter patent discloses a permanent magnet motor including alternating rotor and stator disks, the rotors being affixed to a common shaft. The Felder patent discloses a multiple rotor direct current electric motor.